A pump apparatus includes: a rotational shaft; a hub portion mounted to the rotational shaft; a centrifugal pump vane mounted to a circumferential surface of the hub portion; an annular disc portion mounted to a tip end of the centrifugal pump vane; and an axial turbine blade mounted to an outer circumferential surface of the annular disc portion. A liquid flow passage through which a liquid flowing from a first side toward a second side in an axis direction of the rotational shaft flows into the centrifugal pump vane is formed at a radially inner side of the annular disc portion, and a gas flow passage through which a gas flowing from the second side toward the first side passes through the axial turbine blade is formed at a radially outer side of the annular disc portion.